The present invention relates to a structure suitable for use as an exterior panel of an industrial product such as an automobile and a home electric appliance. More specifically, the present invention relates to a polypropylene-based resin exterior panel which has the same appearance qualities as a coated product though it is not coated and which is excellent in rigidity and impact resistance.
Since the exterior panel of an automobile or a home electric appliance such a washing machine and a refrigerator has been required to have good appearance qualities, a coated steel panel has been generally used as the exterior panel. For the purpose of reducing weight, resin exterior panels have recently been developed. SMC (sheet molding compound) moldings used as the exterior panel of an automobile and polypropylene resin moldings used as a car bumper are coated to fit their appearance qualities to those of coated steel panels.
Particularly, a coated exterior panel for an automobile is coated with a coating containing a reflective flake pigment such as an aluminum flake pigment and a mica flake pigment to provide a metallic or pearly appearance in addition to a regular coloring pigment. By carrying out such metallic coating or pearly coating, there is provided an exterior panel having good appearance qualities such as color tone, color depth and brightness specific to the coating.
However, as these methods require an additional coating step after steel panel pressing or resin molding, it cannot be said that they are economically excellent methods because of a huge amount of initial investment in coating equipment and facilities and a large number of production steps.
To eliminate this coating step, a thermoplastic resin such as PP (polypropylene), ABS (acrylonitrile butadiene styrene copolymer), PC (polycarbonate) or PPO (polyphenylene oxide: Noryl.TM. resin), into which a coloring pigment has been incorporated, is used and molded or injection molded into a sheet to obtain a molding such as an exterior panel directly. Particularly, PP is the most preferable because PP is inexpensive and has good moldability, and colored PP is used in many industrial products.
However, a non-coated product obtained by a method which uses such a colored resin and includes no coating step cannot obtain good appearance qualities such as color tone, color depth and brightness specific to coating. Particularly, it shows inferior quality difference from a coated product, especially in metallic color or pearl color.
In a process for producing a non-coated exterior panel using this colored resin, since a coloring pigment is superfluously dispersed in a whole resin, when an expensive pigment is used, a colored resin itself costs dear and hence, the process is not economical.
There is a proposed process for forming a weatherable polymer cast film comprising a pigment on a polymer substrate as a non-coated resin exterior panel (Japanese Patent Publication No. 4-20782 (U.S. Pat. Nos. 5,536,539, 5,514,427 and 5,342,666)). However, this process is not economical because of its layer structure.
There is also disclosed a resin laminate having a metallic gloss and consisting of a base layer of a polyolefin-based resin, a colored layer, a transparent resin layer and an acrylic ultraviolet-light-cured surface layer (Japanese Patent Publication No. 1-180338: Japanese Patent No. 2546871 (U.S. Pat. No. 5,089,291)). When a base composition is molded by injection molding which has great freedom in shape, the appearance of the laminate may deteriorate with the above layer structure.